Research On Application And Evolution Law Of Pressure Relief Gas Reservoir In Fully Mechanized Caving Mining Of Extra-thick Coal Seam

The distribution of extra-thick coal seams in the west of China is extensive,and the mining height and intensity are high during the recovery,the overburden fracture development height rises and the scope is widened,so the ability to accumulate gas is significantly enhanced,which is easy to cause gas overrun.Accurate extraction of mine gas is one of the effective measures to solve this problem,and clarifying the evolution law of unloading gas storage area of extra-thick coal seam is a prerequisite to realize accurate extraction of mine gas.After exploring the results of structural movement and fracture evolution of mining overburden,unloading gas storage area and extraction methods,the paper concludes that the study of mining overburden movement,stress evolution,fracture distribution and morphological characteristics of extra-thick coal seam is the basis for clarifying the evolution law of unloading gas storage area.The test face of the paper is selected from Binchang mining area,through physical similar simulation experiments and 3DEC discrete element numerical simulation,the overburden movement,stress evolution,fracture distribution and morphological characteristics of mining overburden of extra-thick coal seam are systematically analyzed,and the overburden stress distribution area can be divided into stress concentration area,pressure relief area and original rock stress area,the overburden breakage fracture distribution curve and delamination rate distribution curve are in the shape of The distribution curves of overburden fracture and fracture rate are in the shape of "M" type double hump,and the overburden collapse displacement and fracture form are in the shape of trapezoidal distribution,and the overburden displacement,stress,fracture distribution and morphological characteristics are similar under different mining height conditions,and the peak value of each characterization parameter shows an increasing trend when the mining height increases.Based on the results of physical similar simulation and numerical simulation experiments,the overburden longitudinal fracture and transverse delamination fracture are concentrated in the working face side unloading zone(fracture zone)below the key layer,and the unloading gas storage area can be divided into three categories:high storage area,medium storage area and low storage area,and it is believed that the mining unloading gas storage area usually appears below the key layer in the working face side unloading zone(fracture zone),and its The shape changes with the breakage state of the key layer above;the area of the storage area first rises and then falls,after which it develops periodically,and the peak value increases when the mining height increases,corresponding to the decreasing trend of the advance distance.Based on the elastic foundation beam theory and key layer theory,the method of discriminating the location of unloading gas reservoir area is proposed.The extraction mode of unloading gas extraction is clearly defined as low storage area is mainly by buried pipe or low drilling,medium storage area is mainly by high drilling,long directional drilling or high extraction lane,high storage area is mainly by long directional drilling,high extraction lane and ground drilling,which forms a multi-method collaborative three-dimensional extraction technology system in different areas.According to the engineering practice,the final hole location of high extraction hole should be arranged in the unloading gas storage area as far as possible,the gas concentration in working face,return air alley and upper corner is controlled below 1%,and the unloading gas extraction rate is maintained above 80%,which shows that the arrangement of high drilling hole according to this method is reasonable and ensures the safe and efficient production of working face,and provides a good solution for effective prevention of mine gas disaster,scientific arrangement of gas extraction system and precise extraction of mine gas.It provides a theoretical basis for effective prevention of mine gas disasters,scientific arrangement of gas extraction system and precise extraction of mine gas.